Power semiconductor devices are devices for use in power conversion from alternating current to direct current or direct current to alternating current, and are used in a motor driving apparatus configured to drive a feed shaft and a main shaft of a machine tool, and an arm of an industrial machine and an industrial robot, etc. The power semiconductor device is typically implemented in intimate contact with a radiator, etc. and configured to allow heat generated during power supply to be released to the radiator and make the heat radiate from the radiator into air by natural convection.
In some cases, the heat is efficiently radiated by the radiator to the air by creating air flow using a fan motor and thereby releasing heated air to the outside. Thus, it is possible to suppress temperature rise in the power semiconductor device and fully exploit the capability of the power semiconductor device.
However, the power semiconductor device fails to fully exploit its capability when a malfunction or an abnormality degrading heat dissipation capability occurs in a certain portion of the heat dissipation route of the above-described power semiconductor device. In addition, the power semiconductor device may be damaged when the device is kept in use despite a malfunction or abnormality.
By way of example, the following factors can be cited as possible malfunctions and abnormalities in the heat dissipation route:
(1) Low heat conductivity from a chip of the power semiconductor device to a base metal surface (which may be caused by malfunctioning of the power semiconductor device as such);
(2) Low heat conductivity between the base metal surface and the radiator (which may be caused by omission of application of silicon grease or performance deterioration of the silicon grease over time);
(3) Low heat conductivity of the radiator (which may be caused by clogging of a heat dissipation fin with dust obstructing flow of air, or a dirty surface of the heat dissipation fin degrading heat dissipation capacity).
(4) Insufficient flow of air relative to a desired amount thereof (which may be caused by an abnormality (decrease in rotation speed, stoppage, etc.) of the fan motor).
Various techniques have been proposed in the context of the detection of the above-identified malfunctions and abnormalities. With regard to the first to the third factors cited above, for example, one of the proposed techniques implements a unit adapted for detecting the temperature of the chip of the power semiconductor device and temperature of the radiator as such, and stops the motor driving apparatus when the temperature exceeds a certain specific temperature (for example, see Japanese Unexamined Patent Publication No. JP-A-2011-036095, hereinafter referred to as “Patent Literature 1”).
Patent Literature 1 proposes a method of calculating the temperature of a power semiconductor device while power is supplied thereto and thus protecting the device appropriately. The method of calculating the temperature of the power semiconductor device includes obtaining a sum of a value of temperature measured at a reference point and a calculated value corresponding to the temperature rise in the power semiconductor device relative to the reference point. In the calculation of the temperature rise, thermal conduction of the power semiconductor device is modeled based on the primary delay system.
The related art described in Patent Literature 1, however, relies upon the premise that a malfunction or an abnormality is not to be found in a heat dissipation related route, and that the real temperature is correctly estimated by the calculated value of the temperature of the power semiconductor device. It is accordingly not possible to provide correct calculation and proper protection when a malfunction or an abnormality occurs in the heat dissipation route. In fact, the above related art is not capable of detecting malfunctions and abnormalities of the heat dissipation route.
In addition, the related art described in Patent Literature 1 has such problems as “increase in the cost needed to implement a temperature detection unit”; abnormality detection being only possible when the certain specific temperature has been exceeded”; and “detection of malfunction being only possible for a limited range of portions of the heat dissipation route”.
With regard to the fourth factor cited above, a technique has been proposed that, for example, monitors the state of rotation of the fan motor (rotating or stopped, rotation speed, etc.) and stops the motor driving apparatus when an abnormality is found in the state of rotation. Another technique has been proposed that detects an abnormality of the state of rotation of the fan motor by monitoring a change in the temperature of the radiator while power supply to the motor is disabled (for example, see Japanese Unexamined Patent Publication No. JP-A-2007-312536, hereinafter referred to as “Patent Literature 2”). Since the fan motor is an independent component among those belonging to the heat dissipation route, malfunctions and abnormalities of the fan motor can be relatively readily detected.
Patent Literature 2 discloses an inverter apparatus that detects an abnormality of an air blowing unit such as a fan motor. FIG. 1 partly illustrates a cooling mechanism described in Patent Literature 2. A power semiconductor device module 1009 and a diode module 1007 are mounted on and in intimate contact with a heat dissipation fin 1010 serving as a heat dissipation member. A temperature sensor 1011 adapted to detect the temperature of the heat dissipation fin 1010 is provided on an upper surface of the heat dissipation fin 1010. The heat dissipation fin 1010 comprises multiple fins 1010A, and there is also provided a cooling fan 1012 such that the cooling air flows along the fins 1010A.
In the related art described in Patent Literature 2, an abnormality in the air blowing unit is detected by stopping the power supply after occurrence of a certain amount of a rise in the temperature of the heat dissipation member, and monitoring the occurrence of a subsequent fall in the temperature of the heat dissipation member. Specifically, the abnormality of the air blowing unit is detected based on a difference between a temperature fall in the disabled state and a temperature fall in the enabled state of the air blowing unit.
The above related art may be capable of detecting an abnormality in the air blowing unit (fan motor, etc.) in the heat dissipation related route. It should be noted, however, that there are problems in that an abnormality may only be detected in the air blowing unit; accurate detection is not available when a malfunction occurs in a unit for enabling/disabling the air blowing unit and a unit for detecting the temperature of the heat dissipation member; and that detection cannot be performed unless the power supply is disabled.
In the context of detection of malfunctions and abnormalities of the heat dissipation route that releases the heat generated by the power semiconductor, it has been difficult in the related art to detect “abnormalities of various components involved in heat dissipation in a cost-effective manner” and “at an early stage”. It is therefore an object of the invention to readily detect malfunctions or abnormalities of the components involved in the heat dissipation route of the above-described power semiconductor device with reduced cost for the motor driving apparatus.